Avoiding the Most Common Mistakes on GMAT Data Sufficiency Questions

Written by Kelly Granson. Posted in GMAT Study Guide

GMAT Data Sufficiency mistakesPerhaps you have never seen anything like GMAT Data Sufficiency questions in any other test. You might be surprised, perplexed, or even alarmed; yet, you cannot afford to waste precious time and concentration figuring out how to deal with them. Therefore, read on! We will help you prepare for this very special part of the GMAT.

While answering Data Sufficiency questions on the quantitative section of your GMAT, you are expected to demonstrate ability to identify the information essential for further analysis. In contrast to Problem Solving Questions, you are not required to come up with an actual answer; you only need to figure out whether the information given is sufficient to calculate an answer.

In practice, what you see is a question followed by two statements. Your assignment is to determine whether either of the statements separately or both of them combined can serve as a valid basis for answering the question. Since there is no need to conduct lengthy and intricate calculations to answer the question correctly, it is easy to underestimate the complexity of your task and to lose valuable points.

We recommend that you review below the most common mistakes GMAT-takers make on Data Sufficiency questions, and learn these simple strategies for avoiding them.

Mistake #1: Forgetting to examine each statement separately.

When determining whether information given is sufficient to answer a question, be sure to take a separate look at each statement individually. It's important to see whether either of them by itself provides a satisfactory answer. If you fail to do so, you might end up mixing information from the two statements, then answering that one of the statements is sufficient, when in fact, you would need to use both if you were to answer the question. In order to avoid this mistake, make sure that you "put aside" the information supplied in statement 1 while you check statement 2, and vice versa. If it helps, you can physically cover each of the statements (for example, with your finger, or with a pen) so that it does not distract you.

Mistake #2: Over-calculating.

Sure, when you face Problem Solving Questions, you will need to run all your calculations to a meaningful end to devise a correct answer. However, when doing Data Sufficiency Questions, you do not need to go to all that trouble. You only need to determine whether you CAN give the answer, not what it is. Therefore, if you see an equation with several operations, inconvenient fractions, and other puzzling stuff, but only one variable (x), you do not need to shed sweat and blood deciphering a mass of numbers. The only thing you need to do is to say "Yes, I can devise the answer to this problem," and select the correct answer.

Mistake #3: Under-calculating.

The opposite mistake is being too cursory when dealing with a question. Just as wasting time on calculations can be a problem, failing to do calculations can also be a mistake in GMAT Data Sufficiency. For instance, you might see two statements, each of them being an equation with two variables, and assume that the combined information will provide you with simultaneous linear equations and thus will be sufficient for answering the question. However, the two relations might be disguised variations of a single equation with two unknowns, and there is no way you will be able to solve it! To avoid this mistake, try to do at least several operations on your problems to make sure they really are leading to an answer.

Mistake #4: Confusing a negative answer to the question with insufficiency of data.

Let's assume you are asked, "Are more than half of Genderville citizens female?" and your statement choices are:

(1) There are 78,892 males living in Genderville.

(2) The population of Genderville is under 150,000.

Under the pressure of time and confusion built up from previous complicated questions, some GMAT-takers would tend to answer that the information provided is insufficient for answering the question, when in fact, it is clear that females do not make up more than half of Genderville's population. Do not make this mistake! "No" is a legitimate answer to the question, and both statements combined provide sufficient data to yield such a conclusion.

Mistake #5: Making unwarranted assumptions.

Often, test-takers are tricked by questions that lead to faulty assumptions. For example, to the question, "How many jelly-filled doughnuts are there in a box?" the first statement provides that the number of doughnuts in the box is 12, and the second one states that 6 are filled with cream. Here, you might be tempted think "Well, that's easy! 12-6=6—there's my answer," and check that the data in statements 1 and 2 are sufficient for solving the problem. Yet, this thinking rests on the assumption that all the doughnuts in the box are filled with either jelly or cream, forgetting that those options were not specified! There might have been doughnuts with no filling, some with chocolate filling, caramel, or who knows what else! Hence, to avoid this mistake, you should never assume more than is explicitly stated in a question.

When taking the GMAT, the key to steering clear of the most common mistakes in answering Data Sufficiency questions is to remain focused and attentive. If you remember these mistake-avoidance strategies despite the stress and time-crunch of the test, you will be able to perform to the best of your ability on these complex and oh-so-tricky questions!


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